More events needed to pin down gravitational waves backstory

DUOS’ DANCE Mergers of two pairs of black holes (illustrated) showcase ability of gravitational waves as a new tool for understanding the universe. LIGO detected gravitational waves from both mergers shown, but at different times and in different parts of the sky.

A. Simonnet/LIGO

SAN DIEGO — While astrophysicists celebrate the second detection of ripples in spacetime (SN Online: 6/15/16), they are also looking ahead to figuring out what led to these cosmic quakes. Black holes colliding in remote galaxies sent the gravitational waves our way. But how these duos ended up in an ill-fated embrace in the first place is unknown.

With only two clear detections from the Advanced Laser Interferometer Gravitational-Wave Observatory, and a third marginal candidate, there isn’t enough information to figure out for sure how these binary black holes formed. But there are two leading ideas.

One is that two heavyweight stars, each more than roughly 20 times as massive as the sun, are born, live and detonate together. Their deaths would leave behind a pair of black holes snuggled up to one another. They would eventually spiral together

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